The field of compliant electrical probes involves various designs of spring probes used in the automatic testing of printed circuit boards. In other instances a spring probe of roughly similar design can be used as a compliant connector for making releasable connections in electronic devices such as cellular phones or computers, for example.
In the automatic testing of electrical circuits, test probes of various configurations are used depending upon such factors as the type of electrical device under test, the spacing between test points, and the like. One type of prior art test probe includes a movable plunger mounted in a tubular barrel with the probe end of the plunger extending outwardly from the barrel. A compression spring in the barrel supports the plunger for spring-biased axial travel within the barrel. The plunger is spaced outwardly a selected distance by the spring and may be biased inwardly into the barrel a selected distance under a force directed against the spring. The probe plunger has a probe tip designed with various configurations for making contact with selected test points on the electrical device under test.
The process of making a conventional spring probe involves separately producing the compression spring, the barrel and the plunger. The compression spring is wound and heat treated to produce a spring of a precise size and of a controlled spring force. The plunger is typically heat treated and sometimes the barrels are heat treated. All components are subjected to a plating process to enhance conductivity. The spring probe components are assembled either manually or by an automated process. During assembly, the compression spring is first placed in the barrel, the plunger is then inserted into the barrel to compress the spring, and the barrel is roll crimped to retain the plunger. In use, the completed spring probes are commonly inserted into an outer receptacle for retaining the probe in a fixture or the like. The principal cost factors in producing these multi-component probes are the separate manufacturing costs of the components and the assembly time and equipment for producing the finished part.
U.S. Pat. No. 4,773,877 to Kruger et al. discloses a contact probe for an electronic tester in which the probe includes a one-piece resilient contact pin having a guided plunger at one end and a spring section at the other end. The approach taken in the Kruger '877 patent is intended to reduce spring probe production costs. The plunger section and spring section are integrally joined and formed from a common sheet metal piece. The particular form of the contact probe shown in the Kruger '877 patent would not be useful as an electrical connector for carrying high loads subjected to constant cycling. The Kruger contact probe also would not be useful for high density spring contacts in a miniaturized connector adapted for mounting to a printed circuit board and also subjected to constant cycling.
The present invention overcomes the drawbacks of the Kruger '877 contact probe by providing a solid metal compliant high current carrying electrical connector and, in one form of the invention, by providing solid metal compliant contacts for several forms of miniaturized connectors adapted for mounting to printed circuit boards.
The present invention also provides a unique process for making a one-piece compliant electrical probe with greatly reduced production costs. The costs involved in producing the separate components of traditional spring probes and assembling them into a workable unit are eliminated. In addition, certain functional improvements are provided, including lowering the electrical resistance of the probe, which produces improved capacity for high current carrying applications. The invention also is useful in applications either as a test probe, a compliant connector, or a switch probe.